Pneumatic size gauging device



A. l..v A. FoRTlER PNEUMATIC SIZE GAUGING DEVICE Original Filed Sept. 4, 1947 Oct. 16, 1951 Patented Oct. 16, 1951 QFFl-CE PNEUMATIC SIZE GAUGING DEVICE Andr L. A. Fortier, Clamart, France, assigner to Etavex S. A., a corporation of Switzerland Original application September 4, 1947, Serial No.

1951, Serial No. 228,551

3 Claims. l

'This is a division of my copending application for patent, Serial No. 772,105, filed September 4, 1947, now Patent No. A2,564,527 issued August 14, 1951. V

It is known that it is possible to measure the distance between two adjacent surfaces by means of a ow of gas. For this purpose one of the surfaces is Apierced with a small orifice through which a gas ows. When the other surface is approached towards the `orice, the free cross section afforded to the Vpassage of the gas depends on thezdistance between the two surfaces. Under these conditions, the measurement of the outflow of gas or of the pressure at the upflow of the orifice enables Fthe dista-nce between the two surfaces to be determined. In particular when a calibrated orifice of constant cross section is placed in series with the orifice of variable section, according to lthe position of the two surfaces, the measurement of the resulting pressure p ibetween the two surfaces enables the free cross section of the second orifice to be determined when the pressure is maintained at a given value P at the .upflow of the first orifice and when the pressure at the downflow of the second orice is known, which maybe simply atmospheric pressure p0. When thediiferences in the pressure P-p and` p-po are small relatively to the pressures P, p and p0, the deliveries Q1 through the first orifice and Q2 through the second orifice are proportional `to 'the powersof P-p and p-po which vary from 1 to 1/2 according to the geometrical shape of the cross sections of the two orifices. When equilibrium is established the deliveries Qi and Q2 are equal. Under these conditions, when the pressure P and 100 `are constant, discharge through the upiow orifice being constant, the pressure p is a function lof the magnitude of the section orifice and enables it to be measured after a previous marking by a standard. The second orifice .may be located at a distance d from 'a wall, pis thus the function of d and the measurement of p enables d to be found.

For obtaining correctrresults, it is necessary to maintain the` pressure P constant by means of Va pressure regulator or an expanding device located on the :upflow of the first orifice. i

But the employment of known pressure regulators Vinvolves difficulties. The most precise, of the 'type' provided/with `a container filled with liquid to a constant level into 4which dips a stationary gas inlet tube, are fragile and of little practical yuse for -commercial measurements. The same applies to liquid gauges. Regulators Divided and this application May 28,

or ordinary metal gauges lack sensitveness, accuracy and precision.

It has been proposed, for remedying these disadvantages, to measure the resistance opposed by an orifice to the lpassage of a gas, not directly by the measurement of a pressure p, but by comparison with a known resistance.

One of the best mountings known, for effecting this measurement of comparison, is that shown in Figure 1 in Ia diagrammatic manner. It is the equivalent in the field of mechanics of fluids, to the Wheatstone bridge commonly utilized for the measurement of electrical'resistances.

The main branches l and 2 of this bridge are connected at 3 to a tank of relatively constant pressure P. From the point of connection 3, each branch is provided with two orifices `ll, 5 and 6, 1, respectively, resisting the flow of gas 'and arranged in series, the intermediate sections of the branches forming chambers 8 and 9 between which is located the bridge l0 proper, provided with a differential gauge H, also serving to indicate equality in pressure. The measuring ori-nce is located in proximity to a wall b, while a movable needle 4D yenables the useful cross section to be modified, that it is to say, the resistance of the comparison orifice 5.

The principal advantage of this assembly of Wheatstone bridge is to render the precision of the measurements liable to -be influenced only very slightly bythe value of the pressure P at the upliow and by the temperature, so that it is the same in all the parts of -the apparatus.

But in order that the measurement be precise and independent of P, it is necessary that the gauge vl I, for indicating equality in pressure, be very sensitive. It is necessary, more exactly, for the gauge I-I to be sensitive to smallest difference which might exist between the pressures in the chambers 8 and 9. It is for this reason that it has been proposed heretofore to use as an indicator of equality in pressure between the charnbers a liquid gauge with inclined tubes. Besides its fragility, such a gauge has another serious disadvantage before resistances through the orifices 5 and l are equalized under the influence of pressure P. Such inequalityv of pressure causesthe liquid to beemptied from 'the gauge. It is, therefore, necessary to provide -a tap or bleeder to stop the flow of gas to the sensitive indicator I I While the resistance 5 is adjusted so as to obtain approximate equality of pressures in the spaces 8 and 9. 'This tap plays the part of the switch -of the -electric Whea-tstone bridge which only enables current to be passed ythrough Ythe sensitive galvanometer when equilibrium of the bridge isv already almost obtained. The operation of this tap, which is indispensable and which, however, has not been provided in the assemblies described so far, renders the apparatus practically useless commercially. t

Instead of the liquid gauge with inclined tubes,

' it is possible to use a metal or mechanical gauge of a known type. In this case, although the gauge may resist a considerable difference in pressure, it is necessarily only slightly sensitive and consequently does not afford the full advantages of the Wheatstone bridge assembly. On the other hand, if the gauge is very sensitive and consequently fragile, it is necessary to protect it in such a manner that the larger differences in pressure which exist between the chambers 8 and 9 during the adjustments are not liable to damage it.

The present invention has for its object the provision of a differential pressure indicating device with a deformable diaphragm secured at its periphery or rim and separating two gas chambers, applicable toa measuring assembly similar to that shown in Figure l. This device is distinguished from other known devices in that it is provided, in combination with a Wheatstone bridge assembly, with at least one bearing surface for limiting the maximum deformation of the diaphragm under the action of a resultant pressure, that is, limiting the movement of the diaphragm so that it willnot become damaged and will return to its original'neutral position, this bearing surface being so shaped that, practically the whole of the useful surface of the diaphragm can be applied thereto.

Such a device can resist, without damage, the large differences in pressure while retaining its sensitiveness when the pressures are equalized.

In the accompanying drawing:

Figure 1 is a diagrammatic View illustrating Athe application of the invention to a measuring assembly.

Figure 2 is a cross sectional View of one embodiment of the invention, and

Figure 3 is a similar sectional view of another embodiment.

The parts common to both embodiments will be first described.

A connecting tubular member I2 is connected at one end to an air tank, not shown, in which is maintained a substantially constant pressure P, appreciably higher than atmospheric pressure. The other end of the tubular member is connected to two passages I3 and I4 in shunt, said passages containing calibrated orifices I5 and I6, assumed identical for simplification of the description. The passages I3`and I4 are provided in a casing I'I. The passage I3 leads into a chamber I8 communicating with the atmosphere through a calibrated downflow orice I9 provided in a plate 20 covering the chamber I8; the passage I4 leads into a smaller chamber 2l comunicating with the 'atmosphere through a second calibrated orifice 22.

A differential pressure indicating device, described hereinafter, is interposed betweenr the pneumatic chambers I8 and 2|', which are the equivalent of the respective Ychambers 8 and 9 of lthe Wheatstone bridge'Y assembly shown jecting from the under face 26 of the said trough 24. Consequently the under face 26 is located at a predetermined distance from the bottom of the chamber I8. The trough 24 is provided with a number of perforations 2l distributed uniformly Y and its upper edge is flat; it serves to support the periphery or rim of a circular diaphragm 29 Y normally flat and equallydeformable by pressure from either side thereof.

A second trough 30, substantially similar to the rst, but inverted and provided with perforations 3l, is disposed lon its flat lower edge 32 to the periphery or rim of the diaphragm 29 which is thus clamped between the two troughs, and secured to the casing II by` securing means not shown.

The concave surfaces of the two troughs 24, 3D are located opposite one another and also have the same axis of rotation z-e, coincident with the axis of symmetry of the diaphragm. These concave surfaces are so shaped that they form bearing surfaces for practically' the wholev of the effectively deformable portion of the diaphragm.

The diaphragm 29 carries at its center a boss 33 secured to -a rod 34 passing Vfreely through the upper trough 30 and connected to a resiliently flexible contact bar 35 of which one end is con.- nected -to a. terminal 36. The free end of the contact Abar 35 is located between two conducting blades V3l, 38 clamped in an insulating block 39, but does not touch either when the diaphragm 29 is in neutral position.

Thecalibrated orifice 22 opens at a short distance d from an object b, the dimensions of which it is'desired to measure.

The free cross section of the second orifice is modified by lan axially movable needle or valve stem 40.A

All the members which have been described with reference to Figure 2 occur in the same man- Y ner and similarly combined Vin the apparatus shown in Figure 3. They form -a kind of pneumatic Wheatstone bridge.

The apparatus of Figure 2 which serves to measure automatically, for example, the variations in thickness of a rod b, seen in end view resting on a support M rthat the operator l,moves longitudinally, is also provided with a reversible or electric servo-motor 4I with two directions of rotation of which the field windings, of opposite direction, are connected to blades 31 and 33, respectively. Onepole of the source of vcurrent S is connected directly to the terminal 42 ofthe motor. The other pole is grounded to the casing I'Ibyalead 43. f

A pinion 44, mounted at the end of the shaft of the motor 4I meshes with long internal teeth of a transmission flange 45 which is rotatable about and slidable along the axis 22. The hub 46 of the flange 45 has a screw threadV engaging with a screw-threaded bore 41 of a cover plate f vof the same resistance as that opposed bythe orifice I9 into which'the needle 4D has been moved previously 'into an arbitrary zero position marked bythe scale 48.

The operator moves the rod b Vlongitudinally on the support M. When its thickness varies the distance d likewisevaries and the free cross sec- .aangaf V'si'.ion forli-,he .passageof .air through the orifice 22 is .modiedwhicdin iturn, modifies.r the pressure :in thechamber2 .acting .on the llower face of ethe `lziiapllragm5:29.. When,:.ior example, a lowering fof the sensitive pressure occurs, :the fsaid .dia-

phragm curves. .downwardly itow-ards :the .bottom .and its usefulsnrface bears almostover its .entire area against the .concave :surface 4of the .trough 2'4` which vserves asa support zth'erefor while V.avoidingany deleterious urgingof thediaphragmf 'under .the faction .of 'the difierence in Ipressure :between'the :chambers I 8.and2 l, :that is, :avoiding movement .of 'the Adiaphragm beyond iits:.elastic limit. When @curving `.1in this manner, the-,diaphragm carries with "it fthe bar 35 vwhich .closes the circuit .of 4the motor-4l by .coming .into resilient contact with the v.blade :38. 'The motor il starts, .causing'the ilange 45 to turn, `which produces :an Aaxial ascending Vmovementof the needle 4.5 in fthe `orice |59 until :the rresistance opposed by ith'is oriicehas become equal to .that opposed by .the `orifice-22 Aopposite the bar.

Equilibrium of the .pressures .between the chambers '|18 and i2| `is thus .re-established, the dia- `Aphragm resumes its mean or :neutral position,

seen .in `Figure 2, and-the bar.3i5 moves 4away Ifrom the blade 38. The circuit through members .42, 4|, A38, 3.5, 36, troughs, icasing and lead 43 being broken, the motor 4| stops. During the rotation of the motor 4|, the scale 48 has turned under the pointer 49 by an `amount "which is a function f thefvariaition necessary .of .the-across section of the orice I9 for re-establishing.equilibrium Vof pressures .between the-.chambers i8 and 2| This quantity, read directly on the scale, indicates to the operator how much the distance d .has increased and, consequently, how much `,the thick- -ness e of the bar has decreased, :relatively .to the thickness o-f the -bar in its initial position.

Conversely, when the thickness increases between two successive positions of the bar b, the pressure increases in the chamber 2|, the diaphragm curves upwardly until it bears against the trough 30. The bar 35 closes the circuit of the motor by contacting the blade 31, the motor 4| starts in a direction opposite to its previous direction of rotation, until pneumatic equilibrium is reestablished between the chambers I8 and 2|. The diaphragm 29 returns to its mean or neutral position and breaks the circuit between the blade 39 and the bar 35. The new position assumed by the scale 48 behind the marking pointer 49, enables the increase in thickness e of the bar b to be ascertained from the region measured previously. In continuing the movement of the bar in this manner, then stopping it each time the motor 4| starts until the motor stops automatically, it is possible to control the variation in thickness of the bar over its entire length in a semi-automatic manner.

Even when, involuntarily, the bar is moved suddenly from the orifice 22, the sudden lowering of pressure then produced in the chamber 2| is not liable to damage the diaphragm 29 which simply bears over its entire useful surface against the concave surface of the lower trough 24. The perforations 21 have too small a diameter to enable a thrust of sufcient value to pass therethrough for damaging the diaphragm even when it is thin and, therefore, sensitive.

In the apparatus shown in Figure 3, and which may serve for measuring the dimensions of an object b or of a series of objects, the needle 40 is secured to an operating knob of which the threaded spindle '52 engages with a screw threaded bore :4:1 :of :al-cover plate .220.. .Theronducting Tblades 3.1 :and 3.8 are connected *to two .diierent circuits 5.3, ,5,4 in parallel ina ldistribut- .ing 4network .S. In a very-:simple example, these zcircuits may be :formed luy-,signalling .lamps Vof ,diierent colors. `It will at `once be seen 'that .a variationl'of the dimension of ,anobjectb producing Van increase Vof pressure in ithechamber 2| is translated `by :curving `vof the diaphragm .2.9 upwardly .and by the 'closing of contacts 35, .3l-reisulting inthe lighting .of the lamp 53. The 0perator then actuates the-knob s5.| in sucha direction that the-needle 40 'penetrates considerably into the orifice `|9 ,1,1ntil the-lamp `53 is extinguished, indicatingthe return of the diaphragm A29 to the neutral 4or mean position and the reestablishmentof equilibrium of the fpressures in chambers :|8 and.2|. AReading the 4scale 48 .gives the Anew valve -of the distance d and, therefore, .the variation -in `dimension of the object b.

I-f it is the lamp 54 which lights, the variation of thedimension of the lobject b is inthe opposite direction.

It will -be understood that -the possible applications voi the invention, are numerous, the'applications lshown in `Figures 2.and 3 being illustrations -.only. AIn particular the vdev-ice may be :applied to the `automatic control, for example, `of a truing device. In using the device shown in Figure 3 Yfor this purpose, the contact rblade 31 .is omitted, because the -tr-uing machine, such `as a grinding wheel, operates only `to shorten the dimension. Consequently, control .in only one .direction is necessary.

Fromthe Yforegoing description, it -will fbe seen that the invention has, among others, the following .technical advantages,

1. The possibility of operatingat 4a high pressure, while using a very Ipliant .diaphragm which is very sensitive to small differences in pressure, at the same time being resistant to great differences in pressure between its two faces, which makes it possible to take full advantages of a Wheatstone bridge assembly.

2. The provision of an apparatus of very small dimensions which responds very rapidly to variations in dimensions of the object to be measured or controlled. In fact, an extremely rapid reaction of the apparatus is obtained by reducing the effective volume of the gaseous medium located on the downstream of the orifice I6, by placing this orifice at the outlet of the passage |4 in a cylindrical cavity forming the chamber 2|.

I claim:

1. A pneumatic gauge comprising a casing having a pair of separate gas chambers therein, said chambers having a common wall consisting of a fiat, yieldable, elastic diaphragm of high sensitivity, a pair of perforated concave members straddling and holding the rim of said diaphragm against axial movement, said concave members having a permanent ilxed relationship relative to the neutral position of the diaphragm to abut and thereby limit the axial displacement of the center of the diaphragm within the elastic limit of the diaphragm, each of said chambers having a gas inlet, means for delivering a gas under pressure to said inlets from a common source, each of said chambers having also an outlet, the outlet of one chamber being adapted to be disposed in proximity to a surface of an object to be gauged, the other outlet having an adjustable valve therein to vary the rate of discharge of gas from its corresponding chamber, means connected with said valve for indicating --diierent positions ofl adjustment thereof, means for indicating axialdisplacementofv the center of said diaphragm'from either side'of its neutral position, said last named means being inoperative havinga pair of separate gas chambers therein, said chambers having a common Wall consisting of a hat, yieldable,y elastic diaphragm of high sensitivity, a pair of lperforated concave members lstraddling and vholding the rim of said -diaphragm againstaxial movement, said 'concave members having a permanent xed relationship relative to the neutral position of the diaphragm 'toabut and thereby limit the axial displacement 'of thecenter of the diaphragm Within the elastic limit of the diaphragm, eachof said chambers having a gas inlet, means for delivering a gas under pressure to said inlets from a common source, each of said chambers having also an outlet, the outlet of one chamber being adapted Vtobe disposed in-proximity lto a surface lof an object lto be gau'ged, the other outlet having a ymanually adjustable valve 'therein to vary the -rate of discharge of gas from its corresponding chamber, means connected with said valve for indicating dii-"ferent positions 'of adjustment thereof, means for indicating aXial displace- `ment of the center of said diaphragm from either side of its neutral position, said vlast 'named `means being inoperative when the diaphragm is in its neutral position, said indicating means comprising an operator connected to and movable 1 with said diaphragm. I l

3. A pneumatic gauge comprising av casing lhaving a pair of separate gas chambers therein,

said chambers having a common Wall consisting vof a at, yieldable, elasticv diaphragm of vhigh sensitivity, a pair of perforated concave members straddlingrand holding the rim of said diaphragm against axial movement, said concave members having a permanent fixed relationship relative to the neutral position of the diaphragm to abut and thereby limit the axial displacement of the center of the diaphragm Within the elastic limit of the diaphragm, each of said chambers having a gas inlet, means for delivering a gas under pressure to said inlets from a common source, each of said chambersy having also an outlet, the outlet of one chamber being adapted to be disposed in proximity to a surface of an object to be gauged, the other outlet having an adjustable Y valve therein to vary the rate of discharge of gas from its corresponding chamber, means connected With said Vvalve for indicatingdifferent po-A 'ANDR L. A. FORTIER.

REFERENCES CITED The following references are of record in the le of this patent:

'UNITED STATES PATENTS Number NameV Date l 2,350,058 May May 30, 1944 2,390,252 Hayward Dec. 4, 1945 2,516,932

Wainwright Aug. 1, 1950 

